1. Field of the Invention
The present invention relates to a saw blade for cutting hard workpieces, such as concrete or stone, and more particularly to a saw blade comprising a shank and a plurality of cutting tips attached to the outer circumference of the shank, characterized by improvement of the shape of the shank of the saw blade providing the cutting tips of the saw blade with a rotational force while the cutting tips are securely attached to the shank.
2. Description of the Related Art
As well known to those skilled in the art, a saw blade for cutting workpieces generally comprises a shank of a prescribed diameter and a plurality of cutting tips attached to the outer circumference of the shank. Usually, each of the cutting tips is made of a super-abrasive material which has very high hardness, such as diamond or cubic boron nitride (CBN). The cutting tip may be classified as either a segment-type cutting tip or a rim-type cutting tip, on the basis of the shape with which the cutting tip is attached to the outer circumference of the shank. The segment-type or rim-type cutting tip may have prescribed ribbed portions formed at the front surface of the cutting tip which makes contact with a workpiece and at the side surfaces of the cutting tip which are perpendicular to the front surface of the cutting tip, respectively. The saw blade comprising cutting tips having the aforesaid rugged portions formed thereon is generally called a turbo saw blade.
A cutting device generally comprises a cutting tool for cutting workpieces, a motor for transmitting power to the cutting tool, and an electrical and mechanical apparatus connected to the motor. The saw blade is a kind of cutting tool. The saw blade comprises a shank, which is composed of a disc-shaped body made of prescribed alloy steel, and a plurality of cutting tips attached to the outer circumference of the shank.
The cutting tips are the part of the saw blade which serves to cut the workpiece. Each of the cutting tips is made of a mixture of a super-abrasive material and a bonding agent, the mixture is brought to a high level of wear resistance by processing at elevated temperature with or without pressure such that the cutting tips are fully dense. The super-abrasive material is a material with high hardness, such as diamond or cubic boron nitride (CBN). The bonding agent is composed of metal powder serving to maintain the attachment of the super-abrasive material to the cutting tips, and to assist continuous regeneration of the super-abrasive material in the course of cutting the workpiece.
The cutting tip may be classified as either a segment-type cutting tip or a rim-type cutting tip. The segment-type cutting tip is composed of a sector member having prescribed length, width and height, which is attached to the outer circumference of the shank. The rim-type cutting tip is composed of a ring-shaped member having prescribed width and height, which is also attached to the outer circumference of the shank.
FIG. 1 is a plan view of a conventional saw blade 10. As shown in FIG. 1, the saw blade 10 generally comprises a shank 11 and a plurality of cutting tip 14. The shank 11 is provided at the center thereof with a hole 19 of a prescribed diameter, through which a rotating shaft of a powered tool (not shown) is inserted so that a rotational force from the powered tool is transmitted to the shank 11 via the rotating shaft of the powered tool. The shank 11 is also provided at the outer circumference thereof with a plurality of spaced slots 17, which are uniformly spaced apart from each other by units of the length of the curved cutting tips 14 attached to the outer circumference of the shank 11, so that a prescribed number of the cutting tips 14 are uniformly attached to the outer circumference of the shank 11. The slots 17 serve as passageways through which cooling water is supplied to the saw blade when the workpiece is cut by the saw blade in a wet cutting fashion.
The saw blade 10 with the above-stated construction is manufactured as follows: A super-abrasive material, such as diamond or cubic boron nitride (CBN), and a bonding agent, such as a metal powder, are uniformly mixed to provide a compound of the super-abrasive material and the bond. The compound is poured into a prescribed mold where the compound is compressed, compacted, and sintered to obtain a segment-type or rim-type cutting tip. The cutting tip is attached to the outer circumference of the shank having a prescribed diameter, through silver soldering, welding and sintering processes, whereby a saw blade for cutting workpieces is finally manufactured.
The operation of the saw blade with above-stated construction will now be described. The saw blade is attached to the shaft of a powered tool (not shown) in such a manner that a rotating shaft of the powered tool is inserted into the hole 19 formed at the center of the shank 11 of the saw blade 10. When the powered tool is operated, the shank 11 of the saw blade 10 now securely attached to the rotating shaft of the powered tool is rotated. The rotational force from the shank 11 of the saw blade 10 is transmitted to the cutting tips 14 attached to the outer circumference of the shank 11 of the saw blade 10. When the cutting tips 14 of the saw blade 10 are rotated, a cutting force and a frictional force are generated from the super-abrasive material particles and bond. The workpiece, such as stone or concrete, is cut by means of the cutting force while the cutting tips 14 of the saw blade 10 are rotated.
The cutting force and the frictional force generated between the cutting tips 14 of the saw blade 10 and the workpiece are directly transmitted to the shank 11 of the saw blade 10. The shank 11 of the saw blade 10 vibrates in the direction perpendicular to the cutting direction of the saw blade 10 by means of these forces transmitted to the shank 11 of the saw blade 10. When the cutting force generated in the course of cutting the workpiece is transmitted in the direction of cutting the workpiece, no vibration is generated. When the shank 11 of the saw blade 10 is moved or vibrated in the direction perpendicular to the cutting direction of the saw blade 10 in the course of cutting the workpiece, however, the cutting force is directly transmitted to the shank 11 of the saw blade 10 in the direction perpendicular to the cutting direction of the saw blade 10, whereby large vibration is caused.
When the saw blade 10 is continuously rotated at a high speed of several thousand RPM to cut the workpiece in a dry cutting fashion, the shank 11 of the saw blade 10 is heated to a temperature of several hundred degrees. When the shank 11 of the saw blade 10 is instantaneously heated as mentioned above, the strength of the shank is decreased even though the shank is made of alloy steel. Consequently, the shank 11 of the saw blade 10 vibrates from side to side. When the shank 11 of the saw blade 10 vibrates widely, the shank 11 may be broken or the cutting tips 14 attached to the outer circumference of the shank 11 may be broken off from the shank 11 of the saw blade 10 with the result that a an accident may be caused, for example, an operator of the saw blade may be injured in the course of cutting the workpiece.
In order to solve the aforesaid problems, the prior art includes an improved saw blade which is capable of withstanding the forces transmitted when the workpiece is cut by the saw blade, is shown in FIGS. 3 and 4. The saw blade of FIG. 3 has ribbed portions formed on the shank of the saw blade. The ribbed portions are radially formed from the vicinity of the center of the shank to the outer circumference of the shank in the shape of waves.
As can be seen from FIG. 3, the saw blade 20 has ribbed portions radially formed from the center thereof to the outer circumference thereof. The saw blade 20 comprises a shank 21 and a plurality of cutting tips 24 attached to the outer circumference of the shank 21. As shown in FIG. 4, the saw blade 20 has upper ribbed portions 26 and lower ribbed portions 27, which are radially formed from the center of the shank 21 to the cuttings tip 24 of the saw blade 20.
When a workpiece is cut by the saw blade 20, the cutting tips 24, which make contact with the workpiece, absorb the cutting force, by which the shank 21 of the saw blade 20 is caused to vibrate. When the impact is applied to a straight shank of the saw blade, the shank vibrates seriously. When the impact is applied to a shank of the saw blade having the ribbed portions formed thereon as shown in FIG. 4, however, the vibration of the shank is decreased.
As mentioned above, the cutting force is dispersed in the course of cutting the workpiece by using the saw blade 20 of FIG. 3. However, no clearance is provided at the end part of the outer circumference of the shank 21 of the saw blade 20, which causes friction between the shank 21 and the workpiece. As a result, a frictional load may be induced. The vibration of the saw blade 20 is more serious when the saw blade 20 is attached to a handheld tool giving the possibility that the frictional load induced may be higher. Furthermore, the vibration of the shank is negligible when the shank of the saw blade is small, for example, below 9 inches in diameter. As the diameter of shank of the saw blade is increased the possibility increases that a frictional load will occur between the workpiece and the shank due to the vibration of the shank.
When the frictional load is caused as mentioned above, the cutting speed of the saw blade, which is the most important factor in a small tool, is decreased. Furthermore, the shank is worn and heated due to continuous friction between the shank and the workpiece, whereby the shank may be deformed due to the forces during the cutting work. The result is that an accident may occur.